1. Field of the Invention
The present invention generally relates to a coordinate detecting device which detects a coordinate of an input position and outputs a signal corresponding to the detected coordinate.
2. Description of the Related Art
An input device in a computer system includes a touch panel. The touch panel is installed on a display, and when a user touches a position on the touch panel, the touch panel detects a coordinate position on the display and outputs a signal corresponding to the detected coordinate position.
There is a touch panel to which a user can directly input a predetermined command easily and intuitively.
As the touch panel, there are a resistance film type, an optical type, a capacity coupling type, and so on. Of these touch panels, the resistance film type is generally used because its structure is simple and its control system is easily realized. As to the resistance film type touch panel, there are a four-line type, a five-line type, an eight-line type, and so on, depending on disposition of electrodes on the resistance film.
When the five-line type touch panel is compared with the four-line type and the eight-line type touch panels, in the five-line type touch panel, since a conductive film on an upper substrate disposed at the operating surface side is used only for reading electric potential, a problem of edge sliding, which the four-line type and the eight-line type touch panels have, does not occur. Therefore, the five-line type touch panel is used in environments in which the touch panel is frequently used with hard touches and long-year durability is required.
FIG. 12 is an exploded perspective view of a conventional five-line type resistance film touch panel.
As shown in FIG. 12, a five-line type resistance film touch panel 1 includes an upper substrate 11 and a lower substrate 12. In the lower substrate 12, a transparent resistance film 22 is formed on all the surface of a glass substrate 21, and X axis coordinate detecting electrodes 23 and 24 and Y axis coordinate detecting electrodes 25 and 26 are formed on the transparent resistance film 22. In the upper substrate 11, a transparent resistance film 32 is formed on all the surface of a film substrate 31 and a coordinate detecting electrode 33 is formed on the transparent resistance film 32.
When a voltage is applied to the X axis coordinate detecting electrodes 23 and 24, an electric potential distribution is generated in the X axis direction in the transparent resistance film 22 of the lower electrode 12. At this time, by detecting electric potential of the transparent resistance film 32 of the upper substrate 11, an X coordinate at a position where the upper substrate 11 touches the lower substrate 12 can be detected. When a voltage is applied to the Y axis coordinate detecting electrodes 25 and 26, an electric potential distribution is generated in the Y axis direction in the transparent resistance film 22 of the lower electrode 12. At this time, by detecting electric potential of the transparent resistance film 32 of the upper substrate 11, a Y coordinate at a position where the upper substrate 11 touches the lower substrate 12 can be detected.
In this kind of touch panel, it is necessary to generate a uniform electric potential distribution in the transparent resistance film 22 of the lower electrode 12. In conventional technology, in order to make the electric potential distribution uniform in the transparent resistance film 22 of the lower substrate 12, a method in which electric potential distribution patterns are generated in plural stages around the transparent resistance film 22 is disclosed (for example, see Patent Document 1).
In addition, a method in which a common electrode is formed so as to surround an input surface is disclosed (for example, see Patent Document 2).
[Patent Document 1] Japanese Laid-Open Patent Application No. 10-83251
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-125724
A coordinate detecting device such as a touch panel is required to be small sized due to, for example, miniaturization of an apparatus to which the coordinate detecting device is installed. However, it is difficult for the conventional coordinate detecting device to make its size small due to the installation of the plural stages of the electric potential distribution patterns around the transparent resistance film 22.
In addition, in the method in which the common electrode is formed so as to surround the input surface, when a resistance ratio between the transparent resistance film and pattern resistance is not large, the electric potential distribution of the transparent resistance film is distorted.